Ion chamber amplifier tube



Oct. 29, 1957 N. H. LEHRER ION CHAMBER AMPLIFIER TUBE Filed July 25,1953 I I I l FIG. 5

-2'o -|'o v o +l'0' +20 GRID VOLTAGE R E R H E L H N A M R O N INVENTORATTORNEY United States Patent 2,811,660 ION CHAB/HBERAMPLIFIER TUBENorman H. Lehrer, Bloomfield, N. J., assignor, by mesne assignments, toTung-Sol Electric Inc., Newark, N. 1., a corporation of DelawareApplication July 23, 1953, Serial No. 369,798

4 Claims. (Cl. 313-54) This invention relates to a gaseous conductiondevice having three or more electrodes that may be used as an amplifieror oscillator. It has particular reference to gas-filled devices thatcontainv a quantity of radioactive material which causes continuousionization within the envelope, thereby permitting current to flowbetween the electrodes under application of electrical potentials.

Prior .art discharge devices may be limited by one or more disadvantagessuch as, requiring a filament or heater supply, long stabilization time,minimum operating voltage, and high input power. Other disadvantages mayinclude low amplification and loss of control by the grid electrode onceconduction has been established between the cathode and the anode.

Discharge tubes constructed and operated in accordance with the presentinvention do not conduct electricity between electrodes during thecondition which is commonly called glow or are discharge. The tubes areoperated at voltages which are always less than the value which causes.a glow discharge. Ionization of the gas molecules is caused only by theradiation from the radium or other radioactive material within theenvelope. The pressure in the envelope is high enough to preventionization by collision with the ionized particles and the potentialsused are low enough so that electron field emission and corona dischargecannot occur.

One of the objects of this invention is to provide an improved gaseousconduction device which avoids one or more of the disadvantages andlimitations of prior art arrangements.

Another object of the invention is to provide a gaseous conductiondevice which does not require a heated cathode.

Another object of this invention is to provide a gaseous conductiondevice which can be operated at low voltages and therefore be used incircuits which transmits small amounts of electrical power.

Another object of the invention is to so arrange the ionizing materialwithin the envelope so that the input impedance of the tube is increasedinany times over prior art tubes of similar design.

The invention comprises a gaseous conduction device having three or moreelectrodes. A constant source of ionization, such as radium, is mountedwithin the envelope so as to direct the penetrating radiation toward arestricted space. A control electrode is mounted between an anode and acathode beyond the limits of the restricted space for controlling theamount of current which passes between the anode and cathode.

For a better understanding of the present invention together with otherand further objects, thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

Fig. 1 is a side view of an amplifier tube with some of the parts insection.

Fig. 2 is a cross sectional view ofthe tube shown in Fig. 1 taken alongline 2-2 of that figure.

Fig. 3 is a schematic diagram of connections indicating one of themethods of connecting the amplifier tube shown in Fig. 1. I

Figs. 4 and 5 are graphs to illustrate the electrical characteristics ofa specific example which has been constructed in accordance with thedetails described herein.

Fig. 6 is a cross sectional view of part of an amplifier tube somewhatsimilar to Fig. 1 but showing an alternate arrangement of parts,specifically the arrangement of the mounting which holds the radioactivematerial.

Referring now to Figs. 1, 2, an envelope l0 encloses the tube componentsin a gas tight container. These components include a cylindrical cathode11, a rod-like anode 12, a control electrode 13, and a support 14 for asmall quantity of radioactive material which is placed only on theoutside surface of the electrode. This construction may also includeinsulating spacers 15 and 16, although this form of construction is notnecessary. A base 17 with pins 18 is used for convenient application toan external circuit.

The envelope lltl is filled with a dry gas such as nitrogen -or air at apressure of about 700 mm. of mercury but this pressure may varyconsiderably to a value as high as 5 atmospheres or as low as 300 mm. ofmercury. It has been found by experiment that the best resultsareobtained when a salt of radium such as radium sulphate or radiumbromide is used. It is well known that radiations from any radiumcompound include a considerable percentage of alpha particles which haveintense ionizing properties. It is also common practice to embed theradium material under a very thin coating of gold. This arrangementpermits the ionizing radiation to pass through the film but retains thepoisonous gas Radon from escaping into the air and poisoning workmenduring the assembly process. Other radiation sources may be used insteadof radium, such as radioactive cobalt.

The support 14 is made of a material whose density and thickness issufiicient to absorb the radiations which might otherwise pass to thecentral part of the tube. For this reason the alpha particles and otherionizing radiations will be confined to that region in the tube which isbetween the cathode and the support 14.

When the tube is in operation a layer of ionized gas particles isadjacent to the inner cathode surface while the interior or centralportion of the tube where the grid control electrode and the anode arepositioned is relatively free of ionized particles and for this reasonany potential applied between the control electrode 13 and the cathode11 will produce very little current and this portion of the tube circuittherefore possess a high impedance. Other amplifier tubes somewhatsimilar to this arrangement have been proposed. One such design isdescribed in a patent application by Wilber L. Meier, filed May 11,1953, Serial No. 354,218, and a variation of this design is disclosed ina second application by Wilber L. Meier, Serial No. 354,219, filed May11, 1953. in these tubes the radioactive material is placed in such amanner as to cause ionization throughout the interior of the tube volumeand for this reason the impedance between the control electrode and thecathode is low and the input circuit to the tube when used as anamplifier takes considerable current, thereby reducing the availablevoltage amplification. The present tube restricts the gas ionization toportions adjacent to the cathode surface and in so doing the inputimpedance of the tube is raised more than 20 times above the impedanceof a tube which contains gas ionization throughout its entire volume.

Fig. 3 indicates the manner in which the amplifier tube should beconnected as a voltage amplifier, the input circuit comprisingconnections to the control electrode 13 and the cathode 11. A biasingcircuit with a source of potential 2% and a resistor 21 is connectedbetween the control electrode and the cathode as in other varieties ofamplifier circuits. The output circuit of the amplifier may be derivedfrom a connection to the cathode 11 and the anode 12 although otherforms of output circuits can be used. An anode source of potential 22and an anode impedance 23 may be employed in the usual manner to keepthe anode at an:average positive potential. The support 14 for theradioactive material may be a nonconductor such as mica or a ceramiccomposition but it is usually more convenient to use a metal support andif this is done a lead-in conductor is attached to the support andconnected to one of the pins 18. This pin may then be connected to apart of the anode supply circuit and given a positive voltage which mayvary with the requirements of the circuit and its application. Thisconnection is indicated in Fig. 3 by a dotted line 24.

Figs. 4 and 5 indicate the relationship between the grid voltage and theanode current in one case and the grid voltage and the grid current inthe second case. It should be noted that these curves show a markedsimilarity to the curves which represent the performance of well knowntriodes used in amplifier circuits.

Fig. 6 shows an alternate arrangement of parts and includes an envelope10, a cathodell, an anode .12, and a control electrode 13. The support14 for the radioactive material in this case is a helix which is woundaround the outside of the control electrode and which has radioactivematerial only on its outside surface. Other variations of theradioactive material support will be obvious and may consist of aplurality of rings each similar to the one shown in Fig. 1 or thesupports may be arranged in a vertical alignment, still surrounding thecontrol electrode and containing radioactive material only on the sur- 1face which faces the cathode 11.

The above description has included only that type of conduction devicein which the ionization was restricted to a region adjacent to thecathode. These devices work equally well when the ionization isrestricted to a region adjacent to the anode and excluding the controlelectrode.

Since the envelope contains a quantity of negative electrons andpositive ions the applied potentials may be reversed and the anode andcathode interchanged.

While there have been described and illustrated specific embodiments ofthe invention, it will be obvious that various changes and modificationscan be made therein without departing from the field of the inventionwhich should be limited only by the scope of the appended claims.

I claim: 7

1. A gaseous conduction device comprising; an envelope filled withionizable gas; an anode, a cathode, and a control electrode mountedwithin the envelope; a shield mounted between the control electrode andthe cathode;

and a radioactive material secured to said shield so that ionizingradiation is directed toward the space adjacent to the cathode whileshielding the anode and control electrode from said radiation andpreventing radioactive ionization in the space between the anode and thecontrol electrode.

2. A gaseous conduction device comprising; an envelope filled withionizable gas; an anode, a cathode and a control electrode mountedwithin the envelope; each of said electrodes having a lead-in conductorfor connection to an external circuit; said control electrode positionedbetween the anode and cathode for altering the electric field betweenthem; a metal shield mounted between the control electrode and thecathode; and a radioactive material secured to said shield so thationizing radiation is directed toward the space adjacent to the cathodewhile shielding the anode and control electrode from said radiation andpreventing radioactive ionization in the space between the anode and thecontrol electrode.

3. A gaseous conduction device having a plurality of electrodescomprising; an envelope filled with an ionizable gas; said electrodesincluding an axial anode, a cylindrical cathode, and a controlelectrode; a helical support mounted within the envelope between thecontrol electrode and the cylindrical cathode; and a quantity ofradioactive material secured to said helical support, on the side facingthe cathode, for causing gas ionization in a restricted space adjacentto the cathode surface while shielding the anode and the controlelectrode from said radiation.

4. A gaseous conduction device comprising; an envelope filled withionizable gas at a pressure of more than 30 cm. of mercury; an anode, acathode, and a control electrode mounted within the envelope; each ofsaid electrodes having a lead-in conductor for connection to an externalcircuit; a metal shield mounted between the control electrode and thecathode; and a radioactive material secured to said shield so thationizing radiation is directed toward the space adjacent to the cathodewhile shielding the anode and control electrode from said radiation andpreventing radioactive ionization in the space between the anode and thecontrol electrode.

References Cited in the file of this patent UNITED STATES PATENTS1,145,735 Ainsworth July 6, 1915 2,032,545 McElrath Mar. 3, 19362,266,665 Summers Dec. 16, 1941 2,652,510 Landrey et al Sept. 15, 19532,728,004 Victoreen Dec. 20, 1955

